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Help me identify these conical deposits found in our creek

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I have no idea what these are but they sure look neat. I would really like to put a name on them. I have about another couple dozen of them as well.alt text

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asked Jun 4, 2013 by animalindy (320 points)

4 Answers

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They definitely look interesting! Where did you find them. They look like oddly-shaped sandstone concretions, but some give the appearance of some sort of fossilized shell.

answered Jun 5, 2013 by hershel (47,740 points)

These came out of the creek behind our place. Northwest Arkansas, near the Arkansas River. Lots of caves in the region, but not right here right now. they seem to be a long term drip formation. They are convex on one side and most are concave on the other, though some are relatively flat. I'm pretty certain these aren't sandstone, as they are rough textured but not grainy and are quite solid. nor do they pulverize when struck sharply. I will stick some more pictures in the next answer section.

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some are in my aquarium. the one with my finger in it is to demonstrate concavity, not that it isn't obvious in some of these pictures.

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answered Jun 5, 2013 by animalindy (320 points)
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If there are caves in the area it is also possible they are odd limestone formations formed from water precipitation. Can you test to see if they are limestone (or other carbonate such as dolomite) with an acid test? Do do this, get some strong acid such as Lime Out (available in any Home Depot or similar store), and pour a drop on it. See if it forms tiny bubbles after contact. If it does, then its almost certainly limestone.

answered Jun 6, 2013 by hershel (47,740 points)

I'm looking for identification of form or structure, a specific name. It's certainly not stalactite or stalagmite or I think I would find other forms. They are in a natural creek whose main purpose today is to drain water from a portion of our city streets into the Arkansas River. The biggest one we have found measures 3.5 inches tall, 5.25 inches wide. I wish there was an add picture option in this reply section, because I really don't like answering my own question just to add pictures.

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I don't know what these are called since I have never seen them before. But I am curious to see if they are in fact limestone, and that can be accomplished with an acid test. That can help further understand their formation...

answered Jun 24, 2013 by hershel (47,740 points)
 


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